(3)-(1)得2y+2z=56∴y+z=28 (4)(2)+(4)得2y=31∴y=31/2把y=31/2代入(4)得31/2+z=28z=25/2把y=31/2代入(1)得x-31=-9∴x=22∴方程组的解是x=22y=31/2z=25/2
